Recently, there is proposed a system in which an in-vehicle unit mounted on each of a plurality of vehicles (referred to as host vehicles) wirelessly communicates with the other in-vehicle units existing in a predetermined range from the in-vehicle unit itself without using a wide area communication network. This type of communication between in-vehicle units is generally referred to as inter-vehicle communication.
There is also proposed a system in which an in-vehicle unit to perform the inter-vehicle communication exchanges predetermined information with a service provision terminal (such as a roadside instrument) to provide predetermined services and thereby permit the use of services provided by the service provision terminal. For example, a proposed system causes the in-vehicle unit to provide the service provision terminal with information about the in-vehicle unit itself such as current position information and thereby permit the use of services corresponding to the current position.
Patent Literature 1 discloses an in-vehicle unit that detects a parameter indicating a communication state during communication with other in-vehicle units and detects a predetermined communication error by comparing the detected parameter with a predetermined value. The in-vehicle unit according to Patent Literature 1 diagnoses whether the in-vehicle unit operates normally, based on the number of occurrences of the communication error.